This application claims the priority of Korean Patent Application No. 2002-36443, filed on Jun. 27, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a distributed constant type filter, and more particularly, to a distributed constant type filter having printed circuit boards to remove an electromagnetic wave obstacle.
2. Description of the Related Art
Conventional distributed constant type filters are made up of two facing coils and a parasitic capacitance (C) generated on the area where the two coils overlap. To be more specific, where inductor components adjoin each other in parallel, one coil is used as an inductor electrode, and the other coil is used as a ground electrode. An LC filter is formed by capacitance (C) generated on the area where the two coils overlap. This LC filter forming method is used to manufacture conventional distributed constant type filters.
FIG. 1 shows an equivalent circuit of a conventional distributed constant type filter. Representative conventional distributed constant type noise filters are disclosed in Japanese Patent Publication Nos. hei 8-18377 and hei 8-45745, which are shown in FIGS. 2 and 3, respectively.
The pattern of conventional distributed constant type filters can vary, but the conventional distributed constant type filters with different patterns have a common thing. In other words, all of them have an equivalent circuit of FIG. 1. Referring to FIGS. 2 and 3, the conventional distributed constant type filters disclosed in Japanese Patent Publication Nos. hei 8-18377 and hei 8-45745 have different shapes of patterns but both have the equivalent circuit of FIG. 1.
Referring to FIG. 1, one coil goes into an IN terminal and comes out of an OUT terminal, and another coil, which is under the coil, enters a GROUND terminal. A parasitic capacitance (C) is formed between the two coils.
Referring to FIG. 2, in an A-type pattern, a coil goes into an IN terminal and comes out of an OUT terminal. A-type patterns A1 through A6 are connected to one other to form one coil. B-type patterns B1 through B6 are connected to one other and form a coil that enters a GROUND terminal. The parasitic capacitance (C) of FIG. 1 is generated on the area where the two coils overlap.
A conventional distributed constant type filter of FIG. 3 also has the same structure as shown in FIG. 2. In an A-type pattern, a coil goes into an IN terminal and comes out of an OUT terminal. A-type patterns A1 through A12 are connected to each other to form one coil. B-type patterns B1 through B12 are connected to each other and form a coil that enters a GROUND terminal. The parasitic capacitance (C) of FIG. 1 is generated on the area where the two coils overlap.
To sum up, conventional distributed constant type filters have different patterns in detail but have an identical basic structure. Conventional distributed constant type filters having such an equivalent circuit as shown in FIG. 1 have the following two drawbacks.
Firstly, the inductance (L) values of the two coils and the capacitance (C) value between the two coils must be accurately adjusted to obtain an excellent attenuation curve, but there is a high possibility that a filter with bad attenuation characteristics is manufactured due to a deviation occurring upon a manufacturing process.
Secondly, it is difficult to precisely adjust the L values of the two coils and the C value between the two coils in order to design a filter having different attenuation frequency bands.